<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>监听属性</title>
</head>
<body>
<div id = "app">
    <p style = "font-size:25px;">计数器: {{ counter }}</p>
    <button @click = "counter++" style = "font-size:25px;">点我</button>
</div>
</body>
<script src="../static/js/vue.js"></script>
<script>
    var vm = new Vue({
        el: '#app',
        data: {
            counter: 1
        }
    });
    vm.$watch('counter', function(nval, oval) {
        alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!');
    });
</script>
</html>